1. Field of the Invention
The present invention relates to a control device for controlling an output voltage of a vehicle generator mounted on a vehicle such as a passenger car or a truck.
2. Description of Related Art
In recent years, there is tendency that an engine idle speed is set at a lower value for the purpose of reducing fuel consumption of a vehicle. However, since an output torque of a vehicle engine decrease with its rotational speed, the stability of an idle speed of the vehicle engine is largely affected by drive torque fluctuations of auxiliaries including a vehicle generator belt-driven by the vehicle engine when the engine idle speed is set at a low value. Accordingly, there is known a vehicle-generator control device configured to calculate a power generation torque of a vehicle generator on the basis of an excitation current and rotational speed of the vehicle generator, and to control the excitation current such that an increasing rate of the power generation torque does not exceed a predetermined value, to thereby stabilize the engine idle speed, as disclosed, for example, in Japanese Patent Application Laid-open No. 2003-284257.
However, such a prior art control device has a problem in that undesirable undershoot or overshoot often occurs when a vehicle engine is running at an idle speed, because it cannot detect the excitation current of a vehicle generator at a sufficiently high accuracy, and accordingly the power generation torque of the vehicle generator cannot be detected at a sufficiently high accuracy. In addition, also an output current of the vehicle generator cannot be detected at a sufficiently high accuracy by use of the detected excitation current.